The feasibility of additional <scp>CD19‐targeted</scp> cellular therapy in relapsed/refractory <scp>B‐ALL</scp> with re‐emergence of <scp>CD19</scp> antigen after prior <scp>CD19</scp>‐negative relapse
Authors: Vaibhav Agrawal, Amandeep Salhotra, Joo Song, Zhaohui Gu, Anthony S. Stein, Guido Marcucci, Stephen J. Forman, Vinod Pullarkat, Ibrahim Aldoss
Journal: American Journal of Hematology (2022)

The introduction of CD19-targeted immunotherapies with bispecific T-cell engagers (BiTE) and chimeric antigen receptor (CAR) T-cells has transformed the therapeutic paradigm in relapsed/refractory (R/R) B-cell acute lymphoblastic leukemia B-cell (ALL). While complete remission (CR) rates are high with CD19-targeted immunotherapies, a considerable proportion of R/R B-ALL patients treated with blinatumomab and CD19 CAR T-cell therapy will be either refractory or suffer relapse afterward.1, 2 Therefore, patients with R/R B-ALL will require additional salvage therapies during their disease course. Applying sequential CD19-targeted immunotherapies in R/R B-ALL has proven feasibility, particularly for administering CD19-directed CAR T-cell therapy following treatment failure with blinatumomab. Studies have documented high response rate of CD19 CAR T-cells in R/R B-ALL patients previously treated with blinatumomab, especially if they were previously responders.2-4 Nonetheless, B-ALL relapses after blinatumomab as well as after CD19 CAR T-cells can escape the immune pressure of CD19-target therapy and manifest as a CD19-negative disease. The finding of CD19-negative relapse has crucial implications as it precludes the eligibility for treatment with another CD19-targeted therapy, and, therefore, the patient will be left with limited salvage therapeutic options. Accordingly, the risk of CD19-negative relapse may influence the treating physician's initial choice of CD19-targeted immunotherapeutic strategy. There are several reported mechanisms for developing CD19-negative relapsed ALL after CD19-targeted therapies including CD19 protein truncation or alteration by genetic mutations in exon 2 to 5 of the CD19 gene or alternative mRNA splicing, clonal lineage switch to myeloid phenotype, or outgrowth of pre-existing CD19-negative clones.5, 6 It's yet uncertain if these mechanisms of CD19-negative relapse are persistent or can be reversed during the disease course. We have observed that a fraction of our patients who experienced CD19-negative relapse following blinatumomab could subsequently demonstrate re-emergence of CD19 antigen on later relapses following treatment with alternate targeted therapies. Therefore, we examined a case series of adult patients with R/R B-ALL who were treated with either blinatumomab or/and CD19 CAR T-cells, and then developed CD19-negative relapse. Objectives of the study were to estimate the frequency and predictive factors for re-emergence of the CD19 antigen on subsequent relapse, and to assess the feasibility and activity of administering additional CD19-targeted therapies at the time of CD19 antigen re-emergence. The study was approved by City of Hope Institutional Review Board. Patients were identified through review of medical records of patients who were treated at our institution between 2013 and 2022. We identified 22 adults with R/R B-ALL who were treated with blinatumomab and/or CD19 CAR T-cells and subsequently developed CD19-negative disease. CD19-negative relapse was recorded in 17 (72%) patients after treatment with blinatumomab, one (5%) patient post CD19 CAR T-cell therapy, and four (18%) patients after treatment with blinatumomab followed by CD19 CAR T-cells therapy. The median age at the time of first CD19-negative relapse was 46 years (range: 24–77) and 11 (50%) patients were male. The median number of prior lines of therapies before CD19-targeted treatment resulting in CD19 negative relapse was 1 (range: 0–4), and 4 (18%) patients had relapse after prior allogeneic hematopoietic cell transplantation (HCT). The median duration from the latest CD19-targeted therapy until developing CD19-negative relapse was 168 days (range: 13–787) for all patients, and it was 298 days (range:83–787) after CD19CAR T-cell therapy and 167 days (range:13–614) after blinatumomab. The median follow-up post CD19-negative relapse was 186 days (range: 47–620). After experiencing CD19-negative relapse, the first-line salvage therapy administered was inotuzumab in 12 (55%) patients, clinical trials in 4 (18%) patients, and chemotherapy in 6 (27%) patients. The CR rate to first-line salvage therapy was 46% (n = 10), of which 8 patients received inotuzumab, 1 patient received a clinical trial with CD22-targeted therapy, and 1 patient received chemotherapy. There were 4 additional patients who received inotuzumab after the first-line salvage therapy. Overall, salvage inotuzumab was administered in 16 (73%) patients during the treatment course of CD19-negative relapse with an overall CR rate of 81%. Among responders to salvage inotuzumab, there were 9 patients (41%) that were bridged to subsequent allogeneic HCT, of which 5 patients (56%) have sustained durable remission post-HCT. Among CD19-negative relapsed patients who were treated with salvage therapies and had available CD19 antigen assessment (n = 18) on subsequent relapse or treatment failure, 6 (33%) patients developed re-emergence of CD19-positive disease, of which 3 (50%) were characterized as dim CD19 expression. The median time to CD19 disease re-emergence was 70 (range: 25–557) days. All patients with CD19 re-emergence previously received blinatumomab as the only CD19-directed therapy. Inotuzumab was the last salvage therapy administered in 5 (83%) of these patients prior to observing CD19-positive disease relapse while the remaining patient receiving fludarabine-based chemotherapy. The overall summary of patient characteristics and salvage therapy are described in Table S1. Among these 6 patients with CD19-positive disease re-emergence upon subsequent relapse, 3 (50%) patients were treated with CD19-directed CAR T-cell therapy while the remaining patients did not receive any additional CD19-directed therapy. All 3 patients treated with CAR T-cell therapy achieved negative measurable residual disease (MRD-) CR, with 1 patient successfully bridged to HCT. The first patient was a 61-year-old female with Ph-like ALL with CRLF2::IGH translocation who was treated with blinatumomab for persistent MRD after chemotherapy and achieved MRD- CR. Subsequently, she relapsed with CD19-negative disease and responded to inotuzumab. She underwent allogenic HCT but relapsed early afterward with CD19-positive disease. She received additional inotuzumab and achieved MRD+ CR but suffered central nervous system (CNS) involvement by ALL as well. She was treated with brexucabtagene autoleucel and she achieved MRD- CR in the marrow and the CNS. Unfortunately, she died with septic shock 171 days after receiving CAR T-cells with no evidence of disease relapse. The second patient was a 27-year-old male with Ph-like ALL with CRLF2::IGH translocation who was refractory to initial chemotherapy and then achieved MRD+ CR with blinatumomab. He relapsed after 3 cycles with CD19-negative disease and was then treated with inotuzumab in combination with chemotherapy and achieved MRD- CR2. However, he relapsed with CD19-positive ALL. He received brexucabtagene autoleucel and achieved MRD- CR3, and then underwent consolidation with allogeneic HCT. He is now 144 days post CAR T-cell therapy and in MRD- CR. The third patient was a 75-year-old female with B-cell ALL who responded to initial chemotherapy but subsequently relapsed. She was treated with blinatumomab and achieved MRD- CR2. Subsequently, she relapsed with CD19-negative disease, and she received inotuzumab and attained MRD- CR3. Later, she relapsed with CD19-positive disease, and she then received brexucabtagene autoleucel and achieved MRD- CR4. She is now 53 days post CAR T-cell therapy and in remission. Patient characteristics and response to CD19 CAR T-cell therapy are summarized in Table 1. Herein, we showed that CD19-negative relapse following blinatumomab can be reversible in a subset of treated patients with alternate targeted therapies. In contrast, we did not observe CD19-positive disease re-emergence in any patients previously treated with CD19 CAR T-cell therapy; however, the number of cases relapsed with CD19-negative disease post CAR was small and limits our observation. Nonetheless, this observation could be the result of a deeper response is potentially attained with CAR T-cell therapy compared to blinatumomab, and, therefore, leads to a more profound eradication of CD19-positive clones. Our finding is of a great interest considering the availability of different effective CD19-targeted therapies that could be sequentially effective in R/R B-cell ALL. Among 17 patients previously treated with blinatumomab as the only CD19-directed therapy, our study estimated a CD19 conversion rate of 35% after treatment with inotuzumab. The re-emergence of CD19 antigen could be the result of persistent CD19-positive subclones that became undetectable under the pressure of CD19-targeted therapy that may have expanded later and become the predominant detected clones upon exposure to alternative targeted therapies. The observation of CD19 disease re-emergence following inotuzumab therapy in most cases is of interest and warrants further exploration to understand inotuzumab role in the mechanism of CD19 re-expression. However, the small number of treated patients here limit our interpretation. Additionally, our experience demonstrated comparable high CR rate to inotuzumab in the CD19-negative relapsed B-ALL setting. Most importantly, we have documented the feasibility of administering CD19 CAR T-cells upon re-emergence of CD19 antigen in cases with CD19-negative relapse where other options are extremely limited. Furthermore, the administration of CD19 CAR T-cell therapy led to meaningful response and yielded MRD- remission status in all treated patients, and it has transitioned one young patient to receive a curative allogeneic HCT. Our study is limited by the retrospective nature and the small number of included patients. Furthermore, our study lacked the biological mechanistic explaining this finding, and which patients and what factors influence the re-emergence of CD19 antigen in subsequent relapses. Nonetheless, our observations document that the loss of CD19 antigen is not permanent, at least after treatment with blinatumomab, and allowing for subsequent CD19 CAR T-cell therapy. Our report is important as novel immunotherapies such as blinatumomab are being introduced earlier in the therapeutic paradigm of newly diagnosed B-ALL patients and the burden of CD19-negative relapse is projected to increase and represent an ongoing clinical challenge. Ibrahim Aldoss Advisory boards for Amgen, Kite, Pfizer, Jazz, AbbVie, Sobi, and Agios; Consulting: Pfizer, Autolus, and Amgen. Anthony S Stein is a member of the speakers' bureau for Amgen. Guido Marcucci is a member of the speakers' bureau for AbbVie. Vinod Pullarkat has served on advisory boards for AbbVie and Jazz Pharmaceuticals and is member of the speakers' bureau for Jazz Pharmaceuticals, Amgen, Novartis, and AbbVie. The remaining authors declare no competing financial interests. For original data, please contact [email protected] Individual participant data will not be shared. Table S1: Summary of patient characteristics Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.